We have previously shown that glucose transport is the rate limiting step in glucose uptake and metabolism up to 2 mM glucose in the presence of a maximum insulin concentration and up to 7 mM glucose in the absence of insulin. We now have found that in the presence of insulin above 2 mM glucose, glycogen synthesis, and lactate synthesis become the rate limiting steps. In the absence of insulin above 7 mM glucose, the rate limiting step became lactate synthesis. We now have found that rats made diabetic by streptozotocin have a reduced capacity for glucose transport in the presence and absence of insulin. The glucose concentration over which the rate limiting step changes from glucose transport to a step beyond glucose transport does not change. We are also studying the effect of a high fat diet which has previously been shown to decrease glucose transport and metabolism in adipocytes to see whether muscle transport is similarly decreased and whether this influences the glucose concentration at which transport is no longer rate limiting.